Osteoporosis is a common disease menacing the health of senior people. There are 88,900,000 patients suffering from osteoporosis, which ranks the sixth in all diseases in China in the year 2002. Compression fracture of vertebral body caused by osteoporosis is one of the serious complications. There are 44,000,000 people afflicted with osteoporosis in the United States in 2002. Every year 700,000 out of 1,500,000 fracture cases as a result thereof are spine fractures and half of the patients need hospitalization and surgical treatments. Severe spine fractures may lead to injury of the spinal cord and even paraplegia. The vital capacity decreases by nine percent in the case of compression fracture of one thoracic vertebral body. Mortality of vertebral compression fracture is 23% to 34% within five years. Currently, there are principally two minimally invasive surgical methods for the treatment of the osteoporotic compression fracture of vertebral body:    1. Deramond in France first introduced the percutaneous injection of bone cement into the vertebral body in 1984. The technique is called percutaneous vertebroplasty, and abbreviated as PV. The application of PV for the osteoporotic compression fracture of vertebral body can enhance the strength and stability of the vertebral body, as well as relieve pain. Whereas it can neither increase the height of the compressed vertebral body, nor can it rectify kyphosis. It also has a high leakage rate of the bone cement.    2. Reiley, et al., in the United States designed a technique to rectify kyphosis by means of a new inflation balloon on the basis of inflation balloon of blood vessels in 1994. The technique is called balloon-kyphoplasty and abbreviated as BK. The balloon is inserted into the vertebral body via or from outside of the vertebral pedicle and inflated to restore the height of the compressed vertebral body. A cavity is created inside the vertebral body after the balloon is removed. Then the bone cement is injected into the cavity in the vertebral body. This technique was granted to a U.S. patent under U.S. Pat. No. 5,827,289 in 1998, and was ratified for clinical practice by FDA in 1998. The design purposes of BK are: 1) to restore the height of the compressed vertebral body and rectify kyphosis; and 2) to achieve lower pressure during the injection of bone cement so as to reduce leakage of bone cement. However, a clinical research of BK treatment on 70 vertebral bodies of 30 patients showed that the lost heights were restored by 33.1% and an average restoration was 2.9 mm. The seventy treated vertebral bodies were divided into two groups. One group without height restoration accounts for 30%, and the other group with height restoration accounts for 70%. The average height of the vertebral bodies increases by 4.1 mm, namely by 46.8% in the latter group. Moreover, leakage rate of bone cement is 8.6% in both groups which is similar to that in the treatment of osteoporotic compression fracture of vertebral body by PV. Many other literatures also reported the similar restoration rate of the heights of vertebral bodies and leakage rate of the bone cement. Accordingly, BK has apparently defects in the following aspects:    (1) Clinical practice of BK can only restore on average ⅓ of the lost heights of vertebral bodies. The result is far from the claimed in the design. Patients treated with BK are still obviously kyphotic. As a matter of fact, such a clinical treatment result is predetermined based on the structure of the balloon. According to the principle of hydrodynamics, a pressurized balloon will inflate along the direction of least resistance. Thus, the balloon inflates significantly at the site of fracture, especially at the site of comminuted fracture. Whereas at upper and lower end plates, where restoration to the height of the vertebral body is mostly needed, the inflation is suppressed due to greater resistance.    (2) Leakage rate of the injected bone cement is still relatively high due to the limited restoration in the height of the vertebral body.    (3) Although BK pertains to minimally invasive surgery, the cost of one balloon is very high. This constitutes an enormous economic burden to senior patients suffering from osteoporotic compression fracture of vertebral body. Moreover, since the balloon is easy to be pierced by the sharp bone chips during placement or inflation, the replacement of the balloon is needed, thus aggravating the economic burden on the patients.
Therefore a pressing task in the treatment of osteoporotic compression fracture of vertebral body is to develop a low-cost minimally invasive surgical instrument that not only can substantially restore the lost height of the compressed vertebral body and rectify kyphosis, but also can reduce the leakage rate of the bone cement.